Degradation of the Isoflavone Biochanin A and Its Glucoside Conjugates by Ascochyta rabiei

Strains of Ascochyta rabiei which are pathogenic to chickpea (Cicer arietinum L.) readily catabolized the main chickpea isoflavone biochanin A (5,7-dihydroxy-4'-methoxyisoflavone). 3'-Hydroxylation and O-demethylation reactions led to the isoflavones pratensein, genistein, and orobol, which were rapidly further degraded. Dihydrogenistein and p-hydroxyphenylacetic acid were also identified as catabolites. Biochanin A-7-O-glucoside was degraded, leading to aglycone and pratensein. Biochanin A-7-O-glucoside-6''-O-malonate, the main phenolic constituent of chickpea, was very slowly degraded without subsequent accumulation of catabolites.